One of the fundamental advantage of the GIS is its ability to differentiate the flow direction of each raster pixel. The flow direction in the map of the Bilate catchment is presented in Figure 3 (h). The flow direction is a grid whose value shows how each cell flows with respect to its closest downward slope neighbour (Sanyal 2004). Flow direction was divided into the following five categories: 1–2, 2–8, 9–32, 33–64, and 65–128. Low flow directions imply a high probability of flooding, whereas high flow directions show a low probability of flooding (Table 10). The flow direction ranged (1–2) covered the largest area (48.2%) of the catchment.

Table 10

The flow direction factor of the Bilate catchment

Flow directionArea (km2)Area (%)
1–2 2,734.7 48.2
2–8 1,696 30.2
9–32 664.3 11.8
33–64 301.3 5.4
65–128 228.1 4.1
Total 5,625 100
Flow directionArea (km2)Area (%)
1–2 2,734.7 48.2
2–8 1,696 30.2
9–32 664.3 11.8
33–64 301.3 5.4
65–128 228.1 4.1
Total 5,625 100

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